On slow moving vehicles, such as an agricultural tractor, the hot air which exits the cooling system may be recirculated or re-drawn into the intake of the cooling system. This reduces the potential of the air stream to do useful cooling, thereby increasing the mass of air required for cooling, and as a result, increasing the amount of fan power required. Fan power is parasitic in nature and with the need for improved efficiency, keeping the fan power low is a high priority.
In addition, Tier IV regulations require additional hardware that, if mounted in the engine enclosure, will require a thermal management strategy to prevent damage due to excessive under hood temperatures.
A known vehicle cooling system is described in U.S. Pat. No. 7,051,786 issued on 30 May 2006 and assigned to the assignee of this application. In this system the hood has openings in its upper surface through which passes air blown by the radiator fan unit and the charge air cooler fan unit. This cooling system blows heated cooling air vertically upwardly, thus preventing the heated cooling air from being drawn back into the intakes of the cooling system and preventing heated air from being blown onto the exterior of the tractor cab. However, this system requires multiple cooling units and corresponding electric motor-driven fans to blow air upwardly.
Another known vehicle cooling system is described in U.S. Pat. No. 7,325,518 issued on 8 Sep. 2005 and assigned to the assignee of this application. This cooling system includes a pair of heat exchangers, such as an oil cooler and a charge air cooler, laterally spaced apart from each other and located in front of a front end of the engine. A pair of blower units are in front of the coolers and blow cooling air rearwardly therethrough. A pair of duct units are located above the engine and to the rear of the coolers. Each duct unit includes a forward opening inlet receiving warmed air from the corresponding cooler, an upwardly opening outlet and a hollow housing extending from the inlet to the outlet. The outlets are spaced laterally apart from each other. A radiator is positioned above the duct unit housings and forward of the outlets. A set of radiator fans blow air upwardly through the radiator and are positioned between the radiator and the duct housings. However, with this cooling system, the ducting required to direct the air flow uses up valuable space under the hood. Also, the amount of air movement under the hood was limited.
Most prior and current production tractors do not have enclosed engine compartments. Some prior and current production tractors, such as the John Deere 8030 tractor has ducts that prevent the air from even getting to the engine compartment. Other known production tractors have an enclosed engine compartment, but have significant louvers to allow airflow to exit on the sides.